1. Field of the Invention
The present invention relates to a measuring device and a measuring method for measuring the diameter of a cylindrical object based on a parallax image obtained by making exposures from two viewpoints.
2. Description Related to the Prior Art
Taking a viewpoint image of an observation object from each of two viewpoints a fixed distance apart and indicating a specific point situated on the observation object in each of the viewpoint images allow calculation of a distance from an imaging position to the observation object based on the principle of triangulation, with the use of these viewpoint images as a parallax image.
Likewise, it is also possible to measure the diameter of a cylindrical object by taking two viewpoint images of the cylindrical object from two viewpoints and using the viewpoint images as a parallax image. According to a technique described in Japanese Patent Laid-Open Publication No. 07-139918, a plane orthogonal to a central axis of the cylindrical object is virtually determined from the parallax image. A pair of tangents to a circle, which corresponds to a line of intersection of this plane and a cylindrical surface of the object, is drawn in the plane to obtain the coordinates of each contact point and the coordinates of an intersection point of the pair of tangents. In addition, considering the distance between the two viewpoints, the distance from the imaging position to the cylindrical object, and the like, the diameter of the cylindrical object is calculated.
Also, as is known by Japanese Patent Laid-Open Publication No. 2010-243273, an active method can be used by which viewpoint images are taken from two viewpoints, while light beams are applied to three points situated on the cylindrical object. This method can use light spots of the light beams projected to the cylindrical object together with the parallax image, and has the advantage of permitting the measurement without any inconvenience even if the cylindrical object is inclined in its depth direction.
However, according to the technique described in the Japanese Patent Laid-Open Publication No. 07-139918, an error easily creeps in, in the course of drawing the tangents to each circumferential surface, which is imaged as an outline of the cylindrical object in each viewpoint image, and mathematizing the tangents. Furthermore, in a case where the cylindrical object is imaged in a state of being inclined in a depth direction of the image, an error tends to creep in also in the course of setting the plane orthogonal to the central axis of the cylinder. Also, the technique of the Japanese Patent Laid-Open Publication No. 2010-243273, which has to apply the light beams to a plurality of portions of the observation object, has difficulties such as increase in size of a device and need for much expense in time and effort of initial setting and adjustment.